Lipids are important components of the biological membranes where they are generally thought to exist in the form of bilayers more or less penetrated by protein. Within the proposed project continued systematical studies will be performed to clarify the general structural behaviour of lipids with special reference to cell membrane structure. Different physical methods will be used with the main emphasis on X-ray diffraction. Pure lipids will be studied as well as mixtures of lipids both in the water-free state and in systems with water. The investigation will provide basic knowledge required for an understanding of the molecular architecture of biological systems containing ordered or partly ordered lipid molecules. Particular emphasis is laid on structure and function of sphingolipids which are characteristic components of cell plasma membranes. They participate in lateral hydrogen bonds and thereby influence membrane stability and permeability. Complex glycosphingolipids are of special interest because of their role as antigen determinants and as they are considered to be involved in intercellular recognition and adhesion phenomena. Their pattern changes remarkably during cell differentiation and on transformation to malignant cells.